Create CODEOWNERS file for pull request assignments (#318)

Added CODEOWNERS file to define code ownership for reviews.

Author: jonathanpeppers

.github/CODEOWNERS

@@ -0,0 +1,12 @@
+# android-tools Code Owners File
+#
+# GitHub uses this file to determine who to assign for reviews
+# on pull requests. Please keep this file alphabetically sorted.
+#
+# References:
+#
+# https://github.com/blog/2392-introducing-code-owners
+# https://help.github.com/articles/about-codeowners
+
+# These owners will be the default owners for everything in the repo.
+* @jonathanpeppers @simonrozsival